Filtration — General aspects

The purpose of a filtration operation is to séparation Filtration of a continuous phase (liquid or gas) and a dispersed phase (solid or liquid), initially mixed.

Depending on the case, the aim is to recover :

• or the continuous phase with the dispersed phase removed as far as possible (filtration of air or water, motor oil, edible liquids, etc.);

• or the dispersed phase (recovery of a crystalline precipitate, precious metal dust from fumes, etc.);

• or both phases if their economic interest justifies it.

The two phases can be :

• a gas and a solid (fumes) ;

• a gas and a liquid (fog);

• a liquid and a solid (suspension);

• two immiscible liquids (emulsion).

In what follows, we shall confine ourselves essentially to the study of filtration of liquid-solid mixtures, although many general principles are applicable to other types of filtration. Such a mixture, or suspension, is also known as a prefilter.

Beyond the filter, a more or less purified liquid is recovered, known as filtrate or sometimes mother liquor.